The invention relates to a method for scanning a work piece surface with the aid of a coordinate measuring machine, and to a coordinate measuring machine that is configured, in particular to execute the method. The invention further contains a determining device for determining a value of a movement speed of the coordinate measuring machine.
Coordinate measuring machines are used to measure coordinates of surface points of a work piece. For example, a conventional coordinate measuring machine has a work piece holder for holding the work piece to be measured in a measurement position, and a probe element for scanning the surface of the work piece. In detail, the coordinate measuring machine can have a number of components that can be displaced relative to one another and of which at least one is permanently connected to the work piece holder, and of which at least one other carries the probe element, a plurality of drives for the components being provided in order to displace (that is to say, to move) the probe element relative to the work piece holder. The probe element is, for example, held by a measuring head. It can, furthermore, have a feeler. During scanning of the work piece surface, the probe element is brought into contact with the surface. Once contact has been produced between the probe element and the surface, it is possible to measure the coordinates of the point(s) with which the probe element (which is, for example, spherical) is in contact.
Scanning denotes a specific scanning mode in the case of which measurement points are continuously adopted in order, for example, to measure lines on the surface. During scanning, the probe element is moved on a scanning path, the probe element maintaining its contact with the surface of the work piece.
In particular, as is known from the prior art, in accordance with the present invention the scanning can be executed with the aid of a probe element that, for example, has a sphere that is guided along the surface of the object to be scanned. In this process, a deflection (with reference to the measuring head) of the sphere occurs from its zero or rest position. Moreover, the deflection gives rise to a restoring force that ensures the mechanical contact between the sphere and the object. At which location of the coordinate system the sphere touches the object is calculated from the instantaneous position of the probe element and from the deflection, which can be determined, in particular, with reference to the rest position of the sphere in all possible directions. The deflection is sensed via appropriate displacement sensors on the probe element.
The probe element is moved on the scanning path at a scanning speed. In principle, the scanning speed can vary, that is to say, accelerations and/or decelerations occur during the scanning movement. However, the speed changes can lead to vibrations of the overall system composed of the work piece and the coordinate measuring machine, thus producing measuring errors.
Because of the various drives, a coordinate measuring machine frequently has different maximum possible and/or maximum permissible speeds with reference to the individual degrees of freedom of the movement of the probe element. A degree of freedom of the movement is mostly understood as the possibility of movement on or parallel to a linear axis. For example, a coordinate measuring machine has three mutually independent linear degrees of freedom of the movement when the probe element can be moved in any desired directions at least within a specific measuring range. These three mutually independent linear axes are usually defined as the coordinate axes X, Y and Z of a Cartesian coordinate system. Since the probe element, or the point of the probe element, which comes into contact with the work piece surface can be assumed to be punctiform, and since the orientation of the probe element with reference to a coordinate system in which the work piece is at rest usually does not change during scanning, there is no need to consider further degrees of freedom of the movement, in particular rotary degrees of freedom. However, the invention is not limited to such coordinate measuring machines or measuring arrangements. In particular, the coordinate measuring machine can also have less than three mutually independent degrees of freedom of the movement, and/or at least one of the degrees of freedom can be a rotary degree of freedom, that is to say the probe element can, for example, be guided on a circular track by a rotation about a rotation axis of a drive.